Recently there has been invented a surgical clip which is particularly adapted to occlude or produce necrosis in Fallopian tubes but which could have more general application to humans or to animals, and the clip is called a Hulka clip or a Hulka-type clip. There is a good descripton of the Hulka clip in U.S. Pat. No. 3,882,854, and of a modified Hulka-type clip in UK Patent Specification No. 1,513,650.
In general terms a Hulka-type clip has a pair of pivoted jaws for clamping tissue and a generally U-shaped spring which fits over the jaws and which can be slid forwards from a first position in which the ends of the spring hold the jaws open to a second position in which the ends of the spring (which are turned inwards) engage in recesses near the free ends of the jaw and lock the jaws closed. To guide the spring and prevent it slipping off sideways, it slides in shallow channels on the outside of each jaw, and a Hulka-type clip as referred to herein has such channels. The jaws are referred to as upper and lower jaws for convenience, but in practice the clip can be any side up, depending upon the way up the surgeon is holding the applicator.
Various applicators have been proposed for inserting the clip into the body and locking it over tissue, as described, for instance, in U.S. Pat. No. 3,882,854 or UK Patent Specification No. 1,486,351 - a more recent proposal is disclosed in U.S. Pat. No. 4,169,476. These applicators operate on the same basic principle, namely having a cradle for holding the lower jaw of the clip, a detent for preventing the clip falling out of the cradle and a first ram (which in an intermediate position may act as the detent) for riding along the top of the clip and closing the clip. When the jaw is fully closed, the first ram has passed beyond the locked position of the spring and engages the very front end of the jaw, closing the clip. In practice, the distal end of the first ram engages in the top channel of the clip to prevent the clip falling out of the cradle. There is also a second ram for engaging the rear end of the spring and pushing it forwards into its locking position once the clip has been closed over the tissue by the first ram.
In the case of U.S. Pat. No. 4,169,476 and UK Patent Specification No. 1,486,351, if the first ram has been fully advanced, it will not engage the spring as the spring is pushed forwards by the second ram and trouble-free operation can be expected.
On some occasions, in the use of the applicator of UK Patent Specification No. 1,486,351, there has been high resistance to the forward movement of the spring and hence of the second ram, and the spring has been distorted, leading to a risk that the clip may not be held perfectly closed or may even fall off. The reasons are not certain, but it is believed that on some occasions the surgeon may have allowed the first ram to retract slightly before actuating the second ram; the first ram would then bear on the top of the spring and apply a strong frictional resistance to its forward movement. Another possibility is that the tissue engaged by the jaws may have been too thick, so that the surgeon was unable to push the first ram right forward, with the same effect.